Automatic transmission

ABSTRACT

An automatic transmission of a motor vehicle includes a first rotating element provided by coupling sun gears of a first planetary gear set and a second planetary gear set to each other, a second rotating element provided by coupling carriers of the first and second planetary gear sets to each other, a third rotating element provided by a ring gear of the first planetary gear set, and a fourth rotating element provided by a ring gear of the second planetary gear set. The first rotating element is selectively fixed to a transmission case by a first brake or coupled to an input shaft by a first clutch, and the second rotating element is selectively fixed to the case by a second brake or coupled to the input shaft by a second clutch. The fourth rotating element is coupled integrally to a ring gear of a third planetary gear set, and the third rotating element is coupled integrally to an output gear. With this arrangement, the automatic transmission establishes a selected one of the first-speed through sixth-speed gear stages and a reverse gear stage.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2001-332179 filed onOct. 30, 2001 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an automatic transmission of a motor vehicle,and more particularly to an automatic transmission capable ofestablishing a plurality of gear stages or speeds by using a reducednumber of clutches.

2. Description of Related Art

Automatic transmissions of motor vehicles, each including a plurality ofplanetary gear sets, clutches and brakes, have been widely used.Japanese laid-open Patent Publication No. 2000-199549 discloses anexample of such an automatic transmission which is able to establish sixforward gear stages or speeds by using three planetary gear sets, threeclutches and two brakes.

However, each of the clutches used in the automatic transmissionrequires a drum, seal rings, a mechanism for canceling a centrifugal oilpressure in a cylinder chamber, and other components, for enabling theclutch to be rotated. Thus, the weight and cost of clutches aregenerally greater than those of brakes, and the use of clutches is alsodisadvantageous in terms of the axial length of the transmission.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an automatictransmission capable of providing six forward gear stages or speeds byusing two clutches.

To accomplish the above object, the invention provides an automatictransmission including (a) an input member, (b) an output member, (c) anauxiliary shift portion including a third planetary gear set having asun gear, a carrier and a ring gear, a first one of which is coupled tothe input member, a second one of which is selectively inhibited fromrotating (caused to stop rotating) by a third brake, and a third one ofwhich serves as an intermediate output member and is rotated at areduced speed as compared with that of the input member to output power,and (d) a main shift portion including a first planetary gear set and asecond planetary gear set each of which includes a sun gear, a carrierand a ring gear, at least one of the sun gear, the carrier and the ringgear of the first planetary gear set being coupled to at least one ofthe sun gear, the carrier and the ring gear of the second planetary gearset to provide a first rotating element, a second rotating element, athird rotating element and a fourth rotating element, which are arrangedin the order of description from one end to the other end in a nomogramin which speeds of rotation of the first, second, third and fourthrotating elements are represented by straight lines, the main shiftportion further including a first brake that selectively stops rotationof the first rotating element, a second brake that selectively stopsrotation of the second rotating element, a first clutch that selectivelycouples the first rotating element to the input member, and a secondclutch that selectively couples the second rotating element to the inputmember, the fourth rotating element being coupled integrally to theintermediate output member, the third rotating element being coupledintegrally to the output member. In the automatic transmission, afirst-speed gear stage having the largest gear ratio is established whenthe second brake and the third brake are engaged, a second-speed gearstage having a smaller gear ratio than that of the first-speed gearstage is established when the first brake and the third brake areengaged, a third-speed gear stage having a smaller gear ratio than thatof the second-speed gear stage is established when the first clutch andthe third brake are engaged, a fourth-speed gear stage having a smallergear ratio than that of the third-speed gear stage is established whenthe second clutch and the third brake are engaged, a fifth-speed gearstage having a smaller gear ratio than that of the fourth-speed gearstage is established when the first clutch and the second clutch areengaged, and a sixth-speed gear stage having a smaller gear ratio thanthat of the fifth-speed gear stage is established when the second clutchand the first brake are engaged. The gear ratio mentioned above meansthe ratio of the speed of rotation of the input member to the speed ofrotation of the output member (=rotation speed of the inputmember/rotation speed of the output member).

In one preferred embodiment of the invention as described above, (a) thefirst planetary gear set is a single pinion type, and the secondplanetary gear set is of a single pinion type, and (b) the firstrotating element comprises the sun gear of the first planetary gear setand the sun gear of the second planetary gear set that are coupled toeach other, the second rotating element comprises the carrier of thefirst planetary gear set and the carrier of the second planetary gearset, the third rotating element comprises the ring gear of the firstplanetary gear set, and the fourth rotating element comprises the ringgear of the second planetary gear set.

In another preferred embodiment of the invention, (a) the firstplanetary gear set is of a single pinion type, and the second planetarygear set is of a double pinion type, and (b) the first rotating elementcomprises the sun gear of the first planetary gear set, the secondrotating element comprises the carrier of the first planetary gear setand the carrier of the second planetary gear set that are coupled toeach other, the third rotating element comprises the ring gear of thefirst planetary gear set and the ring gear of the second planetary gearset that are coupled to each other, and the fourth rotating elementcomprises the sun gear of the second planetary gear set.

With the automatic transmission constructed as described above, sixforward gear stages can be established by using three planetary gearsets, two clutches and three brakes. Thus, the weight, cost and theaxial length of the transmission can be reduced as compared with thecase where three clutches and two brakes are used, because of thereduction in the number of clutches.

In the above-described preferred embodiments, three planetary gear setshaving relatively small sizes or diameters can be used, and thetransmission gear ratios of the first-speed through sixth-speed gearstages can be set to appropriate values by suitably determining the gearratios ρ of the three planetary gear sets. In the second preferredembodiment, the carriers and the ring gears of the single-pinion typefirst planetary gear set and the double-pinion type second planetarygear set are coupled to each other, namely, a common carrier and acommon ring gear are used for the first and second planetary gear sets,so as to provide a Ravigneaux type planetary gear train. In this case,the number of components and the axial length of the transmission can befurther reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description ofexemplary embodiments with reference to the accompanying drawings,wherein like numerals are used to represent like elements and wherein:

FIG. 1A is a schematic view showing an automatic transmission of a motorvehicle according to a first embodiment of the invention;

FIG. 1B is an operation table according to which each gear stage of theautomatic transmission of the first embodiment as shown in FIG. 1A isestablished:

FIG. 2 is a nomogram plotted with respect to the automatic transmissionof the first embodiment;

FIG. 3 is a schematic view, corresponding to that of FIG. 1A, showing anautomatic transmission of a motor vehicle according to a secondembodiment of the invention;

FIG. 4 is a schematic view, corresponding to that of FIG. 1A, showing anautomatic transmission of a motor vehicle according to a thirdembodiment of the invention;

FIG. 5 is a schematic view, corresponding to that of FIG. 1A, showing anautomatic transmission of a motor vehicle according to a fourthembodiment of the invention; and

FIG. 6 is a schematic view, corresponding to that of FIG. 1A, showing anautomatic transmission of a motor vehicle according to a fifthembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is preferably applied to an automatic transmission of amotor vehicle, which receives rotary power from a driving power source,such as an internal combustion engine, via a fluid coupling such as atorque converter, changes the speed of rotation at a given gear ratio,and transmits the power from an output member, such as an output gear oran output shaft, to right and left driving wheels, via a differentialgear unit. An input member of the transmission may be a turbine shaft ofthe torque converter, for example. It is to be understood that theinvention may also be applied to automatic transmissions for use insystems other than motor vehicles.

The automatic transmission may be transversely or laterally installedon, for example, a front engine front drive (FF) vehicle, such that theaxis of the transmission extends in the width direction of the vehicle,or may be longitudinally installed on, for example, a front engine reardrive (FR) vehicle, such that the axis of the transmission extends inthe longitudinal or running direction of the vehicle.

The automatic transmission may automatically change its gear ratio orgear stage depending upon vehicle operating conditions, such as anaccelerator pedal position and a vehicle speed, or may change its gearratio in accordance with switching operations (e.g., upshifting anddownshifting operations) by the vehicle operator or driver. Theautomatic transmission according to the invention is able to establishsix forward gear stages, and also establish a reverse gear stage byengaging a first clutch and a second brake (which will be describedlater). While a third planetary gear set (which will be described later)that provides an auxiliary shift portion may be of a double pinion typeor a single pinion type, a double-pinion type planetary gear set ispreferably used for a reduction in the diameter of the gear set when thegear ratio of the auxiliary shift portion is set to about 0.5 so as toset the gear ratios of the transmission in geometric progression. Morespecifically, the double-pinion type third planetary gear set isconstructed as described later such that a sun gear is coupled to androtated by an input shaft of the transmission, and a carrier isselectively inhibited from rotating by a third brake (which will bedescribed), while a ring gear, serving as an intermediate output member,is rotated at a reduced speed as compared with that of the input member,so as to output power. Alternatively, the double-pinion type planetarygear set is constructed such that the carrier is coupled to and rotatedby the input shaft of the transmission, and the sun gear is selectivelyinhibited from rotating by the third brake, while the ring gear, servingas an intermediate output member, is rotated at a reduced speed ascompared with that of the input member.

First through third brakes, first clutch and second clutch as describedlater may be preferably in the form of hydraulically operated frictiondevices of, for example, multiple-disc type, single-disc type or belttype, which are frictionally engaged by means of hydraulic cylinders.Other types of coupling devices, such as those of electromagnetic type,may also be used as the brakes and the clutches. A one-way clutch may beprovided in parallel with the second brake. When an engine brake neednot be applied, the one-way clutch may be provided in place of thesecond brake. Here, one-way clutches function, like brakes, to stoprotation of corresponding rotating members. Other than theabove-described arrangements, the automatic transmission may beconstructed in various ways. For example, a brake and a one-way clutch,which are coupled in series, may be provided in parallel with the firstbrake.

As describer later with respect to the second embodiment, a commoncarrier and a common ring gear are used for a first planetary gear setand a second planetary gear set, so as to provide a Ravigneaux typeplanetary gear train. Alternatively, carriers and ring gears of thefirst and second planetary gear sets are separately provided, and arecoupled integrally to each other via coupling members, or the like.

A main shift portion is preferably constructed in the manner asdescribed later with respect to the first embodiment or the secondembodiment, but various other constructions or arrangements may also beemployed. In one embodiment, for example, the first planetary gear setis of a double pinion type, and the second planetary gear set is of asingle pinion type. In this embodiment, a sun gear of the secondplanetary gear set provides a first rotating element, and a sun gear ofthe first planetary gear set and a carrier of the second planetary gearset that are coupled to each other provide a second rotating element,while a ring gear of the first planetary gear set provides a thirdrotating element, and a carrier of the first planetary gear set and aring gear of the second planetary gear set that are coupled to eachother provide a fourth rotating element.

In another embodiment, the first planetary gear set is of a doublepinion type, and the second planetary gear set is of a single piniontype. In this embodiment, a sun gear of the second planetary gear setprovides a first rotating element, and a carrier of the first planetarygear set and a carrier of the second planetary gear set that are coupledto each other provide a second rotating element, while a ring gear ofthe first planetary gear set provides a third rotating element, and asun gear of the first planetary gear set and a ring gear of the secondplanetary gear set that are coupled to each other provide a fourthrotating element.

In a further embodiment, the first planetary gear set is of a doublepinion type, and the second planetary gear set is of a single piniontype. In this embodiment, a sun gear of the second planetary gear setprovides a first rotating element, and a sun gear of the first planetarygear set and a carrier of the second planetary gear set that are coupledto each other provide a second rotating element, while a ring gear ofthe first planetary gear set and a ring gear of the second planetarygear set that are coupled to each other provide a third rotatingelement, and a carrier of the first planetary gear set provides a fourthrotating element.

The positional relationship between the main shift portion and theauxiliary shift portion and the positional relationship between thefirst planetary gear set and the second planetary gear set of the mainshift portion are not limited to those of the following embodiments, butmay be changed as needed. For example, the first planetary gear set maybe disposed between the third planetary gear set of the auxiliary shiftportion and the second planetary gear set.

Some exemplary embodiments of the invention will be described in greaterdetail with reference to the accompanying drawings. FIG. 1Aschematically shows an automatic transmission 10 of a motor vehicleaccording to the first embodiment of the invention, and FIG. 1B is anoperation table useful for explaining the relationship between engagingelements and gear ratios when a plurality of gear stages of thetransmission are established. The automatic transmission 10 is mountedin the lateral direction in a vehicle, such as a FF vehicle, andincludes a main shift portion 16 and an auxiliary shift portion 20. Themain shift portion 16 mainly includes a single-pinion type firstplanetary gear unit 12 and a single-pinion type second planetary gearunit 14, and the auxiliary shift portion 20 mainly includes adouble-pinion type third planetary gear unit 18. The automatictransmission 10 thus constructed transmits rotary power from an inputshaft 22 to an output gear 24 while changing the speed of rotation. Theinput shaft 22, which corresponds to the above-indicated input member,is a turbine shaft of a torque converter, or the like, which is rotatedor driven by a driving source, such as an engine, for running thevehicle. The output shaft 24, which corresponds to the above-indicatedoutput member, rotates right and left drive wheels via a differentialgear unit. It is to be noted that the automatic transmission 10 isconstructed substantially symmetrically with respect to the center line,and only the upper half of the transmission 10 is illustrated in FIG.1A.

The third planetary gear set 18 that provides the auxiliary shiftportion 20 has a sun gear S3, a carrier C3, and a ring gear R3. The sungear S3 is coupled to and rotated by the input shaft 22, and the carrierC3 is fixed to a transmission case 26 via a third brake B3 to beinhibited from rotating, while the ring gear R3, serving as anintermediate output member, is rotated at a reduced speed as comparedwith that of the input shaft 22, to output power to the main shiftportion 16. Each of the first and second planetary gear sets 12, 14 thatprovide the main shift portion 16 has a sun gear S1, S2, a carrier C1,C2, and a ring gear R1, R2. The first and second planetary gear sets 12,14 provide four rotating elements RM1-RM4 by coupling parts of the gearsets to each other. More specifically, the sun gear S1 of the firstplanetary gear set 12 and the sun gear S2 of the second planetary gearset 14 that are coupled to each other provide a first rotating elementRM1, and the carrier C1 of the first planetary gear set 12 and thecarrier C2 of the second planetary gear set 14 that are coupled to eachother provide a second rotating element RM2, and the ring gear R1 of thefirst planetary gear set 12 provides a third rotating element RM3, andthe ring gear R2 of the second planetary gear set 14 provides a fourthrotating element RM4. The first rotating element RM1 (i.e., sun gearsS1, S2) is selectively coupled to the case 26 by the first brake B1 sothat its rotation is stopped as needed, and the second rotating elementRM2 (i.e., carriers C1, C2) is selectively coupled to the case 26 by thesecond brake B2 so that its rotation is stopped as needed. The firstrotating element RM1 (i.e., sun gears S1, S2) is selectively coupled tothe input shaft 22 via the first clutch CL1, and the second rotatingelement RM2 (i.e., carriers C1, C2) is selectively coupled to the inputshaft 22 via the second clutch CL2. The fourth rotating element RM4(i.e., ring gear R2) is coupled integrally to the ring gear R3 (servingas an intermediate output member) of the third planetary gear unit 18,and the third rotating element RM3 (i.e., ring gear R1) is coupledintegrally to the output gear 24 so as to output power. Each of thefirst through third brakes B1-B3, the first clutch CL1, and the secondclutch CL2 is a hydraulically operated friction device of amultiple-disc type, which is frictionally engaged by means of ahydraulic cylinder. In addition, a one-way clutch F is disposed inparallel with the second brake B2, between the second rotating elementRM2 and the case 26. The one-way clutch F is adapted to allow the secondrotating element RM2 to rotate in the same direction as the input shaft22, but inhibit the same element RM2 from rotating in the reversedirection.

FIG. 2 is a nomogram in which straight lines represent the speeds ofrotation of the respective rotating elements of the main shift portion16 and the auxiliary shift portion 20. In the nomogram of FIG. 2, thelower horizontal line indicates rotation speed “0”, and the upperhorizontal line indicates rotation speed “1.0” which is equal to therotation speed of the input shaft 22. Four vertical lines in the sectionof the main shift portion 16 respectively represent the first rotatingelement RM1 (i.e., sun gears S1, S2), the second rotating element RM2(i.e., carriers C1, C2), the third rotating element RM3 (i.e., ring gearR1), and the fourth rotating element RM4 (i.e., ring gear R2) as viewedfrom the left to the right in FIG. 2. The intervals of these verticallines are determined in accordance with the gear ratio ρ1 (=the numberof teeth of the sun gear/the number of teeth of the ring gear) of thefirst planetary gear set 12 and the gear ratio ρ2 of the secondplanetary gear set 14. Three vertical lines in the section of theauxiliary shift portion 20 respectively represent the carrier C3, thering gear R3 and the sun gear S3 as viewed from the left to the right inFIG. 2. The intervals of these vertical lines are determined inaccordance with the gear ratio ρ3 of the third planetary gear set 18.

As is apparent from the nomogram of FIG. 2, when the second brake B2 andthe third brake B3 are engaged, and rotation of the second rotatingelement RM2 is stopped while the fourth rotating element RM4 is rotatedat a reduced speed via the auxiliary shift portion 20, the thirdrotating element RM3 coupled to the output gear 24 is rotated at a speeddenoted by “1^(st)” in FIG. 2, so that the first-speed gear stage havingthe largest gear ratio is established. When the first brake B1 and thethird brake B3 are engaged, and rotation of the first rotating elementRM1 is stopped while the fourth rotating element RM4 is rotated at areduced speed via the auxiliary shift portion 20, the third rotatingelement RM3 is rotated at a speed denoted by “2^(nd)” in FIG. 2, so thatthe second-speed gear stage having a smaller gear ratio than that of thefirst-speed gear stage is established. When the first clutch CL1 and thethird brake B3 are engaged, and the first rotating element RM1 isrotated as a unit with the input shaft 22 while the fourth rotatingelement RM4 is rotated at a reduced speed via the auxiliary shiftportion 20, the third rotating element RM3 is rotated at a speed denotedby “3^(rd)” in FIG. 2, so that the third-speed gear stage having asmaller gear ratio than that of the second-speed gear stage isestablished. When the second clutch CL2 and the third brake B3 areengaged, and the second rotating element RM2 is rotated as a unit withthe input shaft 22 while the fourth rotating element RM4 is rotated at areduced speed via the auxiliary shift portion 20, the third rotatingelement RM3 is rotated at a speed denoted by “4^(th)” in FIG. 2, so thatthe fourth-speed gear stage having a smaller gear ratio than that of thethird-speed gear stage is established. When the first clutch CL1 and thesecond clutch CL2 are engaged, and the main shift portion 16 is rotatedas a unit with the input shaft 22, the third rotating element RM3 isrotated at a speed denoted by “5^(th)” in FIG. 2, which is equal to therotation speed of the input shaft 22, so that the fifth-speed gear stagehaving a smaller gear ratio than that of the fourth-speed gear stage isestablished. The transmission gear ratio is equal to 1 when theautomatic transmission 10 is placed in the fifth-speed gear stage. Whenthe second clutch CL2 and the first brake B1 are engaged, and the secondrotating element RM2 is rotated as a unit with the input shaft 22 whilerotation of the first rotating element RM1 is stopped, the thirdrotating element RM3 is rotated at a speed denoted by “6^(th)” in FIG.2, so that the sixth-speed gear stage having a smaller gear ratio thanthat of the fifth-speed gear stage is established. When the first clutchCL1 and the second brake B2 are engaged, and the first rotating elementRM1 is rotated as a unit with the input shaft 22 while rotation of thesecond rotating element RM2 is stopped, the third rotating element RM3is rotated in the reverse direction at a speed denoted by “Rev” in FIG.2, so that a reverse gear stage “Rev” is established.

The operation table of FIG. 1B indicates the relationship between therespective gear stages and the operating states of the clutches CL1, CL2and the brakes B1-B3. In FIG. 1B, “◯” indicates engagement, and “⊚”indicates engagement only at the time of application of an engine brake.Since the one-way clutch F is provided in parallel with the second brakeB2 for establishing the first-speed gear stage, the second brake B2 isnot necessarily engaged when the vehicle is started (or accelerated),and the first-speed gear stage can be established only by engaging thethird brake B3. The transmission gear ratios of the respective gearstages are suitably determined depending upon the respective gear ratiosρ1, ρ2 and ρ3 of the first, second and third planetary gear sets 12, 14and 18. For example, if ρ1 is equal to about 0.25, ρ2 is equal to about0.54, and ρ3 is equal to about 0.45, the gear ratios as indicated inFIG. 1B are provided while maintaining the sizes (i.e., diameters) ofthe first, second and third planetary gear sets 12, 14, 16 relativelysmall. As is understood from FIG. 1B, the step value of the gear ratios,namely, the ratio of the gear ratios of the adjacent gear stages, isgenerally appropriate, and the total width of the gear ratios, namely,the ratio of the largest gear ratio to the smallest gear ratio(=4.84/0.80) is a sufficiently large value (which is about 6.05). Thus,the automatic transmission 10 provides appropriate speed-changecharacteristics over the entire range of operation.

With the automatic transmission 10 of the embodiment, six forward gearstages are established by using three planetary gear sets 12, 14, 18,two clutches CL1, CL2 and three brakes B1-B3. Thus, the weight, cost andthe axial length of the automatic transmission 10 are reduced ascompared with the case where three clutches and two brakes are used,because of the reduction in the number of clutches.

Furthermore, the sun gear S1 of the first planetary gear set 12 and thesun gear S2 of the second planetary gear set 14 may be formed as anintegral component, and the carrier C1 of the first planetary gear set12 and the carrier C2 of the second planetary gear set 14 may be formedas an integral component, so that the number of components can bereduced, and the axial length of the transmission 10 can be furtherreduced.

Next, other exemplary embodiments of the invention will be described. Inthe following embodiments, the same reference numerals as used in thedescription of the first embodiment will be used to identifysubstantially the same components or elements, of which no detailedexplanation will be provided.

FIG. 3, which corresponds to FIG. 1A, schematically shows an automatictransmission 30 of a motor vehicle according to the second embodiment ofthe invention. The second embodiment is different from the firstembodiment in the arrangement of a main shift portion 32. The main shiftportion 32 mainly includes a single-pinion type first planetary gearunit 34 and a double-pinion type second planetary gear unit 36, and fourrotating elements RM1-RM4 are provided by connecting parts of the firstand second planetary gear sets 34, 36 with each other. Morespecifically, the sun gear S1 of the first planetary gear unit 34provides the first rotating element RM1, and the carrier C1 of the firstplanetary gear set 34 and the carrier C2 of the second planetary gearset 36 are coupled to each other to provide the second rotating elementRM2. The ring gear R1 of the first planetary gear set 34 and the ringgear R2 of the second planetary gear set 36 are coupled to each other toprovide the third rotating element RM3, and the sun gear S2 of thesecond planetary gear set 36 provides the fourth rotating element RM4.In this embodiment, the automatic transmission 30 takes the form of aRavigneaux type planetary gear train in which the carriers C1, C2 areformed as a common member, and the ring gears R1, R2 are also formed asa common member while a pinion gear of the first planetary gear set 34also serves as a second pinion gear of the second planetary gear set 36.

The first through fourth rotating elements RM1-RM4 are coupled directlyor selectively via brakes B1-B3 or clutches CL1, CL2, to correspondingmembers to provide the same coupling arrangement as that shown in FIG.1A. The automatic transmission 30 thus constructed operates according tothe nomogram as shown in FIG. 2 and the operation table as shown in FIG.1B, so as to establish the first-speed through sixth-speed gear stagesand one reverse gear stage. The transmission gear ratios of therespective gear stages are suitably determined depending upon therespective gear ratios ρ1, ρ2 and ρ3 of the first, second and thirdplanetary gear sets 34, 36 and 18. For example, if ρ1 is equal to about0.25, ρ2 is equal to about 0.46, and ρ3 is equal to about 0.45, the gearratios as indicated in FIG. 1B are provided.

The automatic transmission 30 as described above is able to establishsix forward gear stages or speeds by using two clutches CL1, CL2 andthree brakes B1-B3, and therefore the weight, cost and the axial lengthof the transmission 30 can be advantageously reduced as in the firstembodiment. In addition, since the single-pinion type first planetarygear unit 34 and the double-pinion type second planetary gear unit 36provide the Ravigneaux type planetary gear train, the number ofcomponents and the axial length of the transmission 30 can be furtherreduced.

FIG. 4, which corresponds to FIG. 1A, schematically shows an automatictransmission 40 of a motor vehicle according to the third embodiment ofthe invention. The third embodiment is different from the previousembodiments in the arrangement of a main shift portion 42. The mainshift portion 42 mainly includes a double-pinion type first planetarygear unit 44 and a single-pinion type second planetary gear unit 46, andfour rotating elements RM1-RM4 are provided by connecting parts of thefirst and second planetary gear sets 44, 46 with each other. Morespecifically, the sun gear S2 of the second planetary gear unit 46provides the first rotating element RM1, and the sun gear S1 of thefirst planetary gear set 44 and the carrier C2 of the second planetarygear set 46 are coupled to each other to provide the second rotatingelement RM2. The ring gear R1 of the first planetary gear set 44provides the third rotating element RM3, and the carrier C1 of the firstplanetary gear set 44 and the ring gear R2 of the second planetary gearset 46 are coupled to each other to provide the fourth rotating elementRM4.

The first through fourth rotating elements RM1-RM4 are coupled directlyor selectively via brakes B1-B3 or clutches CL1, CL2, to correspondingmembers to provide the same coupling arrangement as that shown in FIG.1A. The automatic transmission 40 thus constructed operates according tothe nomogram as shown in FIG. 2 and the operation table as shown in FIG.1B, so as to establish the first-speed through sixth-speed gear stagesand one reverse gear stage. The transmission gear ratios of therespective gear stages are suitably determined depending upon therespective gear ratios ρ1, ρ2 and ρ3 of the first, second and thirdplanetary gear sets 44, 46 and 18.

The automatic transmission 40 as described above is able to establishsix forward gear stages or speeds by using two clutches CL1, CL2 andthree brakes B1-B3, and therefore the weight, cost and the axial lengthof the transmission 40 can be advantageously reduced as in the first andsecond embodiments.

FIG. 5, which corresponds to FIG. 1A, schematically shows an automatictransmission 50 of a motor vehicle according to the fourth embodiment ofthe invention. The fourth embodiment is different from the previousembodiments in the arrangement of a main shift portion 52. The mainshift portion 52 mainly includes a double-pinion type first planetarygear unit 54 and a single-pinion type second planetary gear unit 56, andfour rotating elements RM1-RM4 are provided by connecting parts of thefirst and second planetary gear sets 54, 56 with each other. Morespecifically, the sun gear S2 of the second planetary gear unit 56provides the first rotating element RM1, and the carrier C1 of the firstplanetary gear set 54 and the carrier C2 of the second planetary gearset 56 are coupled to each other to provide the second rotating elementRM2. The ring gear R1 of the first planetary gear set 54 provides thethird rotating element RM3, and the sun gear S1 of the first planetarygear set 54 and the ring gear R2 of the second planetary gear set 56 arecoupled to each other to provide the fourth rotating element RM4.

The first through fourth rotating elements RM1-RM4 are coupled directlyor selectively via brakes B1-B3 or clutches CL1, CL2, to correspondingmembers to provide the same coupling arrangement as that shown in FIG.1A. The automatic transmission 50 thus constructed operates according tothe nomoogram as shown in FIG. 2 and the operation table as shown inFIG. 1B, so as to establish the first-speed through sixth-speed gearstages and one reverse gear stage. The transmission gear ratios of therespective gear stages are suitably determined depending upon therespective gear ratios ρ1, ρ2 and ρ3 of the first, second and thirdplanetary gear sets 54, 56 and 18.

The automatic transmission 50 as described above is able to establishsix forward gear stages or speeds by using two clutches CL1, CL2 andthree brakes B1-B3, and therefore the weight, cost and the axial lengthof the transmission 50 can be advantageously reduced as in the previousembodiments.

FIG. 6, which corresponds to FIG. 1A, schematically shows an automatictransmission 60 of a motor vehicle according to the fifth embodiment ofthe invention. The fifth embodiment is different from the previousembodiments in the arrangement of a main shift portion 62. The mainshift portion 62 mainly includes a double-pinion type first planetarygear unit 64 and a single-pinion type second planetary gear unit 66, andfour rotating elements RM1-RM4 are provided by connecting parts of thefirst and second planetary gear sets 64, 66 with each other. Morespecifically, the sun gear S2 of the second planetary gear unit 66provides the first rotating element RM1, and the sun gear S1 of thefirst planetary gear set 64 and the carrier C2 of the second planetarygear set 66 are coupled to each other to provide the second rotatingelement RM2. The ring gear R1 of the first planetary gear set 64 and thering gear R2 of the second planetary gear set 66 are coupled to eachother to provide the third rotating element RM3, and the carrier C1 ofthe first planetary gear set 64 provides the fourth rotating elementRM4.

The first through fourth rotating elements RM1-RM4 are coupled directlyor selectively via brakes B1-B3 or clutches CL1, CL2, to correspondingmembers to provide the same coupling arrangement as that shown in FIG.1A. The automatic transmission 60 thus constructed operates according tothe nomogram as shown in FIG. 2 and the operation table as shown in FIG.1B, so as to establish the first-speed through sixth-speed gear stagesand one reverse gear stage. The transmission gear ratios of therespective gear stages are suitably determined depending upon therespective gear ratios ρ1, ρ2 and ρ3 of the first, second and thirdplanetary gear sets 64, 66 and 18.

The automatic transmission 60 as described above is able to establishsix forward gear stages or speeds by using two clutches CL1, CL2 andthree brakes B1-B3, and therefore the weight, cost and the axial lengthof the transmission 60 can be advantageously reduced as in the previousembodiments.

While the invention has been described with reference to exemplaryembodiments thereof, it is to be understood that the invention is notlimited to the exemplary embodiments or constructions. To the contrary,the invention is intended to cover various modifications and equivalentarrangements. In addition, while the various elements of the exemplaryembodiments are shown in various combinations and configurations, whichare exemplary, other combinations and configurations, including more,less or only a single element, are also within the spirit and scope ofthe invention.

1-10. (canceled)
 11. An automatic transmission, comprising: an inputmember; an output member; an auxiliary shift portion including a thirdplanetary gear set having a sun gear, a carrier and a ring gear, a firstone of which is coupled to the input member, a second one of which isselectively inhibited from rotating by a third brake, and a third one ofwhich serves as an intermediate output member and is rotated at areduced speed as compared with that of the input member to output power;and a main shift portion including a first planetary gear set and asecond planetary gear set each of which includes a sun gear, a carrierand a ring gear, at least one of the sun gear, the carrier and the ringgear of the first planetary gear set being coupled to at least one ofthe sun gear, the carrier and the ring gear of the second planetary gearset to provide a first rotating element, a second rotating element, athird rotating element and a fourth rotating element, the main shiftportion further including a first brake that selectively stops rotationof the first rotating element, a second brake that selectively stopsrotation of the second rotating element, a first clutch that selectivelycouples the first rotating element to the input member, and a secondclutch that selectively couples the second rotating element to the inputmember, the fourth rotating element being coupled integrally to theintermediate output member, the third rotating element being coupledintegrally to the output member, wherein: the first planetary gear setis of a single pinion planetary gear; the second planetary gear set isof a double pinion planetary gear; the first rotating element is the sungear of the first planetary gear set; the second rotating element is thecarrier of the first planetary gear set and the carrier of the secondplanetary gear set that are coupled to each other; the third rotatingelement is the ring gear of the first planetary gear set and the ringgear of the second planetary gear set that are coupled to each other;and the fourth rotating element is the sun gear of the second planetarygear set.
 12. The automatic transmission according to claim 11, whereinthe first planetary gear set and the second planetary gear set provide aRavigneaux planetary gear train in which the carriers of the first andsecond planetary gear sets are formed as a common carrier, and the ringgears of the first and second planetary gear sets are formed as a commonring gear.
 13. The automatic transmission according to claim 11,wherein: the third planetary gear set is of a double pinion planetarygear; and the sun gear of the third planetary gear set is coupled to theinput member, the carrier of the third planetary gear set is selectivelyinhibited from rotating by the third brake, and the ring gear of thethird planetary gear set is rotated at a reduced speed as compared withthat of the input member to output power.
 14. An automatic transmission,comprising: an input member; an output member; an auxiliary shiftportion including a third planetary gear set having a sun gear, acarrier and a ring gear, a first one of which is coupled to the inputmember, a second one of which is selectively inhibited from rotating bya third brake, and a third one of which serves as an intermediate outputmember and is rotated at a reduced speed as compared with that of theinput member to output power; and a main shift portion including a firstplanetary gear set and a second planetary gear set each of whichincludes a sun gear, a carrier and a ring gear, at least one of the sungear, the carrier and the ring gear of the first planetary gear setbeing coupled to at least one of the sun gear, the carrier and the ringgear of the second planetary gear set to provide a first rotatingelement, a second rotating element, a third rotating element and afourth rotating element, the main shift portion further including afirst brake that selectively stops rotation of the first rotatingelement, a second brake that selectively stops rotation of the secondrotating element, a first clutch that selectively couples the firstrotating element to the input member, and a second clutch thatselectively couples the second rotating element to the input member, thefourth rotating element being coupled integrally to the intermediateoutput member, the third rotating element being coupled integrally tothe output member, wherein: the first planetary gear set is of a doublepinion planetary gear; the second planetary gear set is of a singlepinion planetary gear; the first rotating element is the sun gear of thesecond planetary gear set; the second rotating element is the sun gearof the first planetary gear set and the carrier of the second planetarygear set that are coupled to each other; the third rotating element isthe ring gear of the first planetary gear set; and the fourth rotatingelement is the carrier of the first planetary gear set and the ring gearof the second planetary gear set that are coupled to each other.
 15. Theautomatic transmission according to claim 14, wherein: the thirdplanetary gear set is of a double pinion planetary gear; and the sungear of the third planetary gear set is coupled to the input member, thecarrier of the third planetary gear set is selectively inhibited fromrotating by the third brake, and the ring gear of the third planetarygear set is rotated at a reduced speed as compared with that of theinput member to output power.
 16. An automatic transmission, comprising:an input member; an output member; an auxiliary shift portion includinga third planetary gear set having a sun gear, a carrier and a ring gear,a first one of which is coupled to the input member, a second one ofwhich is selectively inhibited from rotating by a third brake, and athird one of which serves as an intermediate output member and isrotated at a reduced speed as compared with that of the input member tooutput power; and a main shift portion including a first planetary gearset and a second planetary gear set each of which includes a sun gear, acarrier and a ring gear, at least one of the sun gear, the carrier andthe ring gear of the first planetary gear set being coupled to at leastone of the sun gear, the carrier and the ring gear of the secondplanetary gear set to provide a first rotating element, a secondrotating element, a third rotating element and a fourth rotatingelement, the main shift portion further including a first brake thatselectively stops rotation of the first rotating element, a second brakethat selectively stops rotation of the second rotating element, a firstclutch that selectively couples the first rotating element to the inputmember, and a second clutch that selectively couples the second rotatingelement to the input member, the fourth rotating element being coupledintegrally to the intermediate output member, the third rotating elementbeing coupled integrally to the output member, wherein: the firstplanetary gear set is of a double pinion planetary gear; the secondplanetary gear set is of a single pinion planetary gear; the firstrotating element is the sun gear of the second planetary gear set; thesecond rotating element is the carrier of the first planetary gear setand the carrier of the second planetary gear set that are coupled toeach other; the third rotating element is the ring gear of the firstplanetary gear set; and the fourth rotating element comprises the sungear of the first planetary gear set and the ring gear of the secondplanetary gear set that are coupled to each other.
 17. The automatictransmission according to claim 16, wherein: the third planetary gearset is of a double pinion planetary gear; and the sun gear of the thirdplanetary gear set is coupled to the input member, the carrier of thethird planetary gear set is selectively inhibited from rotating by thethird brake, and the ring gear of the third planetary gear set isrotated at a reduced speed as compared with that of the input member tooutput power.
 18. An automatic transmission, comprising: an inputmember; an output member; an auxiliary shift portion including a thirdplanetary gear set having a sun gear, a carrier and a ring gear, a firstone of which is coupled to the input member, a second one of which isselectively inhibited from rotating by a third brake, and a third one ofwhich serves as an intermediate output member and is rotated at areduced speed as compared with that of the input member to output power;and a main shift portion including a first planetary gear set and asecond planetary gear set each of which includes a sun gear, a carrierand a ring gear, at least one of the sun gear, the carrier and the ringgear of the first planetary gear set being coupled to at least one ofthe sun gear, the carrier and the ring gear of the second planetary gearset to provide a first rotating element, a second rotating element, athird rotating element and a fourth rotating element, the main shiftportion further including a first brake that selectively stops rotationof the first rotating element, a second brake that selectively stopsrotation of the second rotating element, a first clutch that selectivelycouples the first rotating element to the input member, and a secondclutch that selectively couples the second rotating element to the inputmember, the fourth rotating element being coupled integrally to theintermediate output member, the third rotating element being coupledintegrally to the output member, wherein: the first planetary gear setis of a double pinion planetary gear; the second planetary gear set isof a single pinion planetary gear; the first rotating element is the sungear of the second planetary gear set; the second rotating element isthe sun gear of the first planetary gear set and the carrier of thesecond planetary gear set that are coupled to each other; the thirdrotating element is the ring gear of the first planetary gear set andthe ring gear of the second planetary gear set that are coupled to eachother; and the fourth rotating element is the carrier of the firstplanetary gear set.
 19. The automatic transmission according to claim18, wherein: the third planetary gear set is of a double pinionplanetary gear; and the sun gear of the third planetary gear set iscoupled to the input member, the carrier of the third planetary gear setis selectively inhibited from rotating by the third brake, and the ringgear of the third planetary gear set is rotated at a reduced speed ascompared with that of the input member to output power.